Radio navigation system



June 4, 1946.

Filed may 28, 1941 P. J. HOLMES 7 RADIO NAVIGATION SYSTEM 3 Sheets-Sheet2 76 ins; NGL. METEQ a 8 2.,- COUPL/NG- 6ALAA/CE0 v i MOOULATOESMODULATION Sumac/=- TRANSFOEMEz l-uu.

WAVE RECT/HEK INVENTOR- f?4uL (I H01. MES,

ATTORNEY.

Julie 4, 1946. v

P. J. HOLMES v RADIQ NAVIGATION SYSTEM Filed May 28, 1941 5 Sheets-Sheet5 INVENTOR: "J /10L 1:75 HOLMES,

ATTORNEY.

Patented June 4, 1946 RADIO NAVIGATION SYSTEM Paul J. Holmes, LosAngeles, Calif., assignor of one-half to Richard R. Stoddart, LosAngeles,

Calif.

Application May 28, 1941, Serial No. 395,595

8 Claims.

a radio navigation system utilizing stationary directive antennae havingdiiferently oriented response patterns, such a loop antennae with theiraxes crossed at 90.

A primary object of the invention is to provide a radio navigationsystem for obtaining simultaneous bearings on a plurality of spacedradiators radiating radio carrier waves of different frequencies.

Another object of this invention is to provide a radio compass systemutilizing fixed directional antennae having differently orienteddirectional characteristics which may be mounted on a metal airplane andwhich will give indications which are substantially free from errorordinarily produced by the action of the wings and fuselage on incomingradio Waves.

Numerous direction finders have been proposed which .use stationarydirective antennae havin differently oriented response patterns, such asloop antennae with their axes crossed at 90". However, thesetheoretically superior systems are not in general use and systems usinga directional antenna which is mechanically rotated to indicate thelocation of a transmitting station are most commonly employed. Themechanical rotating of a loop antenna on modern aircraft usuallyrequires considerable flexible shafting, operating motors, relays,saturated reactors, and high-powered amplifiers (usually includinggaseous discharge tubes). This increases the weight of the installationconsiderably and introduces numerous installation and maintenanceproblems. For example, great care must be taken to prevent bendingflexible shafting about a short radius. A another example, difficulty isusually encountered in keeping the flexible shafting lubricated at highaltitudes since most greases tend to congeal at low temperatures.

Special mechanical movements are usually required for linking theflexible shaiting to the loop antenna so that the directional errorsproduced by the wings and fuselage can be compensated for. Thedirectional errors produced by the wings and fuselage have probably beenthe greatest obstacle in the way of preventing the use of crossedstationary loop antennae.

Another object of the invention is to provide a radio compass of thetype described having an electro-mechanical indicating means producingunique directional indications as distinguished from indications havinga possible 180 ambiguity.

Another important object of the invention is to provide a radionavigation system, for follow- 'ing a line in space passing through apair of spaced radiators operating at difierent carrier frequencies.

Further objects and advantages of the invention will be specificallybrought out as the description proceeds or will be apparent therefrom.

My invention will be better understood when described in connection withthe accompanying drawings, in which:

Fig. 1 is a wiring diagram of a typical radio compass according to myinvention;

Fig. 2 is a plan view of a typical all metal airplane on which theapparatus of Fig. 1 may be installed;

Fig. 3 is a'partial front elevation of the airplane illustrated in Fig.2;

Fig. 4 is a front elevation of one of the phase angle indicatorsillustrated in Fig. 1;

Fig. 5 is a diagrammatic plan view illustrating the practice of theinvention in navigation; and

Fig. 6 is a partial circuit diagram illustrating a modification.

Referring to Fig. 1 of the drawings, the apparatus is shown ascomprising a pair of 90 crossed loop antennae l and 2, connected tosupply a radio frequency carrier current to balanced modulators 3 and 4of generally conventional construction. The balanced modulators are fedby modulation currents in phase displaced relation. for example in phasequadrature, from a modulation current source 5 operating at any desiredlow frequency, for example, 100 cycles per second. The modulation source5 is shown connected directly to the balanced modulator 3, and to themodulator 4 through a phase shifter 6 producing,

, for purposes of example, a 90.phase shift of the by the crossed loopsI and 2 are also received by a non-directional antenna 8 and areresupplied to the side band in the coil 1 by means of a coil 9inductively coupled to the coil 7. A pick up coil l l inductivelycoupled with the coil l and 9 feeds the products from the balanced modwlators and the non-directional antenna (the side bands from themodulators plus the re-supplied carrier wave or waves) to a demodulatorl2 where the resultant modulated carrier Wave is demodulated to producea current of the modulation frequency.

It is well known, as evidenced by Luck Patent No. 2,208,378 of July 16,1940, that the phase angle between the current of modulation frequencyin the output of the demodulator l2 and the current supplied by thesource 5, is indicative of the direction between the plane of either oneof the crossed lops, forexample the loop 2, and the position of thesource of carrier waves. Thus the current of modulation frequencyproduced by the demodulator i2 is fedto a suitable phase angle meter l3where it may be compared in phase to the current fed to the balancedmodulators by the modulation source 5.

The system described above differs in two important respects from thesystem'disclosed in the above-mentioned Luck patent. The indications areproduced on an electro-mechanical indicator, thus reducing spacerequirements and eliminating considerable apparatus, and the circuitsare so adjusted as to compensate for the directional errors such asproduced by a metal airplane.

The indicator I3 is shown as comprising field coils Id and I5 fed inphase quadrature by the modulator source 5 through a reactance l6 and aresistor ll respectively. The coils I l and iii are arrangedmechanically to produce a rotating field for an iron armature 18 whichis free to rotate in this field. The iron armature is energized tomagnetically polarize its ends oppositely by means of a coil l9 fed fromthe output of the demodu lat-0r I 2. Thus the iron armature will seek arest position indicative of the phase between" the current of modulationfrequency received from the demodulator and the current of modulationfrequency fed to the coils l 4 and by the modulation source 5... Thearmature may be in the form of a pointer or maybe linked to a suitablepointer to indicate phase or direction from 0 to 360 on a suitablescale. The mechanical construction of the above-described indicator maybe com- I parable to thatemployed for the well-known iron vane phasemeters employed in alternating current power circuits. In Fig. 4 theindicator I3 is shown in front elevation. The calibrated dial isindicated at i311 and the pointer is indicated at The crossed loopantennae I and 2 are indicated diagrammatically in Figs. 2 and 3 in atypical location on an all-metal airplane 2| having wings 3| andfuselage 32. With reference to the appearance of the structure in planview (Fig. 2), the loop antennae are preferably located near theintersection of the fuselage and. the wings and with the planes of theloop antennae l and 2 respectively parallel and perpendicular to thelongitudinal axis of the fuselage, the intersection of the planes of theloop antennae being preferably so located as to intersect substantiallyperpendicularly the longitudinal axis of the fuselage. Thenon-directional antenna 8', usually comprising a short verticallyextending post or rod is usually located on the longitudinal axis of theshorted turn produced by the fuselage is more effective in producingcurrents than the shorted turn produced by the wing. I have found thatthe effects produced by the wings and fuselage may be compensated forwhen the loop antennae are located substantially symmetrically withrespect to the plan profile of the wings and fuselage, by operating thebalanced modulator 4, which is connected to the loop antenna 2, with ahigher gain than the balanced modulator 3.

The balanced modulators 3 and 4 are shown respectively provided withsuitable gain controls 24 and 25 for varying the amplitude of the sidebands produced by a given radio frequency signal introduced into thebalanced modulators by the loop antennae. For example, the gain controlsmay comprise means for varying the control grid or screen grid voltageson the modulating tubes. As another example they may comprise means forvarying the plate voltages applied to the modulator tubes. The gaincontrols 24 and 25 are preferably adapted for concurrent control inopposite directions. The means for effecting concurrent control,comprising any expedient well known in the art, is indicated by thedotted line 26.v Thus movement of the gain control 24 to increase thegain'of the balanced modulator 3 is accompanied by the movement of thegain control 25 to decrease the gain of the balanced modulator 4. Thedirection of movement for increased gain is indicated by the ,arcuatearrows on the gain controls.

In practice the desired relation in gain of the balanced modulators isobtained by tests com I ducted while the airplane is onthe ground. Theplane is orientated so that its longitudinal axis and the plane of loopantenna l makes a definite known angle with a line joining theintersection of the loop antennae and known radiating station. Thesystem is operated so that the bearing of the radiator may be observed.The relative gain of the modulators is then varied to reduce thedifference between the observed bearings and the known bearings to aminimum. This procedure may be repeated for different positions of theairplane or with differently located radiators in order that the mostoptimum relation between the gains in the modulators may be obtained.

In the preceding I have described a system for obtaining bearings on asingle radio station. I have found that with slight modification thesystem may be used to obtain simultaneous bearings on a plurality ofradio stations. Such modification may consist in adding means fordemodulating Waves associated with additional carrier waves, as byadding additional demodulators in parallel with demodulator l2 of Fig. 1according to the number of additional stations on which bearings are tobe had. For example, I may add a demodulator 3| which is adapted todemodulate carrier waves of different frequencies than those demodulatedby demodulator l2.

A suitable phase indicator 32 may be associated with the output ofdemodulator 3| to compare the phase of the current of modulationfrequency with the phase of the current derived from the modulationsource 5. The phase indicator 32 may be constructed in the same manneras the indicator l3 and may be connected to the demodulator 3| and themodulation source 5 in the same manner as the indicator I3 is connectedto the demodulator l2 and the modulation source 5. Obviously, otherdemodulators and phase angle indicators may be added to the apparatus inthe same manner.

It should be apparent that tuned circuits are associated with themodulators and demodulators for obtaining operation on carrier waves ofthe desired frequency. When only a single carrier wave is to be receivedthe circuits need only be responsive to a single carrier wave frequency.When a plurality of carrier waves are to be received and separatelydemodulated, the portion of the circuit before the demodulators isadapted to receive and operate on carrier waves of diiierent frequencieswithin a band of frequencies, for example 150-400 kc., i. e., it isbroadly tuned, while the demodulators are each tuned to select adiiferent carrier frequenc while rejecting others, i. e., they aresharply tuned. It should be evident that the number of carrier wavesreceived is limited by the band width to which the circuit before thedemodulators can be tuned. This general type of system needs no furtherdescription since the same general type of tuning has been employed inradio receivers using untuned radio frequency amplifiers before tuneddetector circuits.

Referring to Fig. 5, a plurality of radio transmitters are positioned toradiate carrier waves of difierent frequencies from the positionsindicated at A, B, and C. An airplane equipped with apparatus such asshown in Fig. 1 for giving simultaneous hearings on the three radiatorsA. B, and C is located at the point 50. The dials of the three phaseindicators are represented by-the circle 5| and the pointers on thedials which are adapted to represent the locations of the radiatorsA, B,and C are designated at a, b, and 0, respectively. At the position 50the angular relation between'the' pointers b. and 0 correspond to theangles between the dot-dashed lines 52, 53, and 54 joining the point 50with the respective radiators A, B, and C. In view of the fact that thedistances between the radiators A, B, and C and their angular relationsare known, the relative angular positions of the pointers a, b, and c isindicative of the absolute location of the point 50 as will be obviousto those skilled in the art of navigation. 7

A primary advantage of the arrangement illustrated in Fig. 5 lies indirecting an airplane to a particular objective. For example, it may bedesirable to direct an airplane to a point for the bombing of anobjective at that point. In such a case, the radiators A and B arealined so that the straight line 56 passing through them also passesthrough the point 55. This alinement may be accomplished b usingportable transmitters at A and B, or one of the transmitters may befixed such as transmitter A, and the transmitter B may be moved to placethe line 55 on the objective. When the airplane is on the line 56 as atthe point 51, the pointers a and b will show the same phase anglereading, while the pointer 0 will show a different phase angle reading.The phase difference between the pointer 0 and the pointers a or b isindicative of the position of the point 51 on the line 56. A particularvalue of this phase difference will occur at the point 55 indicatingthat the pilot has reached the point 55.

The type of system described in Fig. 5 is extremely valuable even thoughthe third radiator C and the phase angle indicating means represented bythe pointer c is omitted, since the line passing through the radiators Aand B produces a clear-cut path which the airplane may follow to anobjective which may be located visually or by other means. When thesystem is operated in this manner the phase angle indicators l3 and 32may be combined in a single indicating device. For example, the movingsystems of each indicating device may be connected to concentricpointers operating on a single indicating dial. If such .is the-case, aposition on the line is indicated when the two pointers give the samephase angle reading. Furthermore, the pointers will show ac-v cording tothe phase angle reading whether. the,

airplane is headed toward or away from the stationsAand B.

As another example, the outputs of the demodulators l2 and 3| may becombined in a single phase angle meter, for example, in the meter l3.Thus, the output of the demodulator l2 maybe connected to the movingcoil is as shown and the fixed coil system may be connected to theoutput of the demodulator 3| instead of the demodulator 5. When theairplane is located on the line 56 the phase angle reading will be. zeroand deviations from one side tothe other 1' anced modulators, as it iswhen the apparatus is usedto obtain -a unique bearing on a singleradiator or simultaneous bearings on three .or more radiators. It shouldbe obvious that when the plane is flying along. the line 55, thedirectional errors with respect to the radiator A are the same as thosewith respect to the radiator B, and since the desired indication is thedifference between the bearings on the two radiators the errors in thesystem cancel. It should also be noted that the flying of a course alongthe line 56 is unaifected by angular headings. produced by the wind. Theposition of the plane on the line is indicated irrespective of theplanes headmg. 7 I 6 Uniform scale divisions on the phase angle metersmay be used when the modulation currents are supplied to the balancedmodulators in phase quadrature, and this relation is preferable when itis desired to obtain bearings on a single radi ator or the simultaneousbearing on a plurality of radiators to determine the absolute positionof the airplane. For those operations it is desirable that the phaseshifter 6 introduce a phase shift in the modulation current supplied tothe modulator 4. However, under some circumstances, as for example whenthe system is used to fly a course such as along the line 55, it may bepreferable to supply the modulation currents to the balanced modulatorswith a phase difierence other than 90, for example or more. This accuses7 will result? inlincreasing dicating instrument by spreadingthescale-readings/over part of the: range and will decrease the.sensitivity of the instrument'by crowdingthescale readings over anotherportion of the vrange. By proper arrangementof-:the apparatus theincreased 7 sensitivity may be obtained :over that part of theinstrument range-indicatingthe-low course position. V

It should be evident V tem maybe obtained without thenon-d-irectio'nalantenna 8; fUnder such circumstance's the output of thedemodul-atorswill be waves of twice modulation frequency.- To obtain 'aphase angle reading the frequency'oi the modulationcurrent from themodulation source-may be; doubled; This may be accomplished as indicatedin Fig." 6 by connecting the imodula'tion source 5 to the phaseindicator or indicators through a full'wave rectifier 6iandtuned:transformer 62? "A suit aisle filter may be employedif'desir'ed. Without the-antenna B the phase angle readings are -subject to a 180 ambiguity. However; this'isnot so serious when theindicator is used in connectionwith a compass to fi acoursefas definedby: the line passing throughftwo spaced-radiators'o eratingat amateurcarriei 'frequencis; VT

Although I have "shown 'separate"demodiil'ators in Fig. I it should beapparentthatf th dernodus l'ators may be'cornbine'd ina'single'demodulating means adapted 'to"sep'arate 'the'modulation meanssuch as'shown herein l. 'l'.n' ccmbin a tion with fan airplane havingmetal wings andfuselage' a directive radio-re:

ceiving'system jcarried on the airplanei compris ing: a firstloopantenna withfits planeisubstantia lly parallel to the longitud a a is ofne r-'1; plane fuselage; a secondgloop antenna Withits planesubstantially a right angled: to: the] plane.

'of the first loop antenna, said antennae being'lo cated onthe'vlairplanei'na position where theerror produced by the.wingsandfiuselage is sub".

st-antially symmetrical aboutsaid position; a d e-l modulator; anon-directive antenna; .a local: source of modulation currents; afirstbalanced modulator connected to receive carrier currents iromthefirst loop antenna; a second balanced modulator having higher gain thanthefirst bal anced modulator and, connected to receivecan.

the sensitivity of the -inthat operationfar the- 's ys ofthe-first'loop' antenna, said antennae being located'onthe airplane in aposition where the error-produced by the Wings and fuselage issubstantially symmetrical about said position; a demodulator; anon-directive antenna; a local source of modulation currents; a firstbalanced modulator connected to receivecarrier. currents lrom 'the:first loop'antenna; asecond'balanced; modulator i connected to receivecarrier currents from the second'loo-p antenna; means for'varying thegains of said modulators concurrently in opposite directions; means forapplyingmodulation currents from said source to said modulators inquadrature phase; means for combining the outputs of said modulatorswith the carrier currents from said non-directional antenna and feedingthem to said demodulator; and phase-= e responsive means connectedto'th'e output 01" the demodulator ior'producing indications of thephase difference between currents of 'modu' lation frequency produced bythe modulation source and: the currents from the'i demodulator.

.In combination with an airplane having 'metal wings and fuselage, adirective radio-receiv'ing system carried onthe airplane," comprising: afirst loop antenna with itsplane substan tially parallel tothellongitudinalaxis of the air-- plzihe'fuselageja second loop antennawithits cplanesubst'antially at right 'angles'to theplane 0f the firstloop antenna, said antennae being located on the airplane inaposition'where the errorproduced by the wings andfuselage is substantia'lly symmetrical about said position; a de-' y modulator; a no'ndirective' antenna; a local source of modulation currents; a firstbalanced mcdulator connected to receive carrier currents from the first'lo'op antenna; a' second balanced modulator having higher gain than thefirst bal anced modulatorand connectedto receive carrier currents fromthe second loop antenna; means for applyingmodulation currents from saidsource to, said modulators in quadrature phase; means for; combining theoutputs of said modu f lators with the carrier currents from said non-jdirectional antenna and feedihg'thm tof id g l:

; modulator; and electro-mechanicalphase-angle frequency produced by themodulation source rier currents: fromthee-second loop antenna;v

means for applying modulation currents from said source .to saidmodulators in quadrature phase; means for combining theroutputs-of saidmodulators with the carrier currents from said non-directional antennaand feeding them to said demodulator; and phase-angle responsive meansconnected to the output of the demodulator for producing indications ofthe phase difierence between currents of modulation frequency producedby the modulation source and the cur-rents from the demodulator. c

2. In combination with an airplane having metal wings and fuselage, adirective radio-receiving system carried on the airplane, comprising: afirst loop antenna with its planesubstanplane substantially at rightangles to the 'plane' responsive means connected to the output of thedemodulator for producing indications of the phase difference between"currents" of modulation and the curi'ents from the demodulator. l

V 4. In combination with an airplane having metal wings and fliuselage,a directional radio-re; ceiving system carried on the airplane,compris-' ing: a first antenna having substantiallya figureof eighthorizontal directivity pattern; a second antenna having substantially afigure-of-eight 1 horizontal directiyity pattern, said-al'itnna'beinglocated with their patterns intersecting substanmany at right anglesadjacent the intersection of the longitudinal axes of the wings andfuselage and with the horizontal directivity pattern of the firstantenna alined for maximum response in a direction substantially alongthe longitudinal axis 7 -01 the, fuselage; a demodulator; anon-directive antenna; a local source of modulation currents; afirst'balanced modulator connected to receive carrier currents from thefirst antenna; a second balanced'modulator having higher gain than thefirst balanced modulator and connected to receive carrier currents fromthe second antenna; means for applying modulation currents from saidsource to said modulators in quadrature phase; means for combining theoutputs-of said modulators with the carrier currents from saidnon-directional antenna and feeding them to said demodulator; andphase-angle responsive means connected to the output of the demodulatorfor producing indications of the phase diiierence between currents ofmodulation frequency produced by the modulation source and the currentsfrom the demodulator.

5. In the operation of an airplane having metal Wings and fuselage of adirectional radioreceiving system of the type in which a pair ofbalanced modulators are fed modulation currents out of phase from alocal modulation source and are fed carrier currents from carrier Wavesintercepted by a pair of loop antennae located in a position on theairplane where the directional errors produced by the airplane aresubstantially symmetrical with respect to said position, one of saidantennae having its plane substantially parallel to the longitudinalaxis of the fuselage and the other having its plane substantiallyperpendicular thereto, the method of minimizing the directional errorsintroduced by the wings and fuselage, comprising: operating the systemto obtain a bearing on a source of carrier waves having a known bearing;and then varying the gain of at least one of the balanced modulators toreduce to a minimum the difierence between the bearing obtained and theknown bearing.

6. In the operation of an airplane having metal Wings and fuselage of adirectional radio-receiving system of the type in which a pair ofbalanced modulators are fed modulation currents in quadrature phase froma local modulation source and are fed carrier currents from carrierwaves intercepted by a pair of loop antennae located in a position onthe airplane which is substantially symmetrically disposed with respectto the plan profile of the airplane, one of said antennae having itsplane substantially parallel to the longitudinal axis of the fuselageand the other having its plane substantially perpendicular thereto, themethod of minimizing the directional errors introduced by the wings andfuselage, comprising: operating the system to obtain a bearing on aradiator of carrier waves having a known bearing; varying the gain of atleast one of the balanced modulators to reduce to a minimum thedifference between the bearing obtained and the known bearing: andrepeating the 10 above operation with radiators having different knownbearings.

'7. In combination with an airplane having metal wings and fuselage, adirective radio-receiving system carried on the airplane, comprising: apair of loop antennae arranged with their planes substantially at rightangles to one another and located on the airplane in such a positionthat the error produced'by the wings and fuselage is substantiallysymmetrical about said position; a local source of modulation currents;a first balanced modulator connected to receive carrier currents fromone of said loop antennae; a second balanced modulator connected toreceive carrier currents from the other loop antennae; means for varyingthe gain of one of said modulators in relation to the gain of the othermodulator; means for applying modulation currents from said source tosaid modulators in quadrature phase; a demodulator; means for combiningthe outputs of said modulators and feeding them to said demodulator; andphaseangle responsive means connected to the output of the demodulatorfor producing indications of. the phase difference between currents ofmodulation frequency produced by the modulation source and the currentsfrom the demodulator.

8. In the operation on an airplane having metal wings and fuselage of adirectional radioreceiving system of the type in which a pair ofbalanced modulators are fed modualtion currents out of phase from alocal modulation source and are fed carrier currents from carrier wavesintercepted by a pair of loop antennae located in a position on theairplane where the directional errors produced by the airplane aresubstantially symmetrical with respect to said position, said antennaehaving their planes substantially perpendicular to one another, themethod of minimizing the directional errors introduced by the wings andfuselage, comprising: operating the system to obtain a bearing on asource of carrier waves having a known bearing; and then varying thegain of one of said modulators relative to the gain of the othermodulator to reduce to a minimum the diflerence between the bearingobtained and the known bearing.

' PAUL' J. HOLMES.

